The present invention relates to a screw inspection device having a parts feeder and transfer means for sequentially transferring screws through a predetermined transfer path while maintaining the screws in a predetermined posture.
With the development of automatic assembly devices, automatic screw fasteners have been recently used widely. When an automatic screw fastener is fed with defective screws, the automatic screw fastener is rendered inoperative. Therefore, the operation of the automatic screw fastener must be temporarily stopped to remove the defective screws or to perform other repair operations. This adversely affects the related manufacturing line and causes a tremendous damage. In order to avoid the above problem, various inspection devices are incorporated into the automatic screw fastener. A roller type sorter 10 which is employed in a conventional screw inspection device is shown in FIGS. 1A and 1B. The roller type sorter 10 transfers a screw a and sorts in accordance with the diameter of the screw head. FIGS. 1A and 1B show the basic members for explaining the structure and function of the roller type sorter. As shown in these figures, the roller type sorter 10 has two rollers 12 of the same shape. The two rollers 12 are disposed so that extended lines of their axes cross with each other. The ends which are close to the crossing point of the extended lines are disposed lower than the ends which are away from the crossing point. A gap between the ends of the rollers 12 which are close to the crossing point, is narrower than that between the other ends thereof. In particular, symbol d1 denotes the gap between the upper ends and symbol d2 denotes the gap between the lower ends, in which gap d1 is narrower than gap d2. The two rollers 12 rotate so that opposing surfaces of the rollers 12 move upward, that is, the rollers 12 rotate in opposite directions. Gaps d1 and d2 and the length of the rollers 12 are selected in accordance with the diameter of the screw head to be inspected. When the screw a is fed to and supported by the circumferential faces of the upper ends of the rollers 12, the head of the screw a is supported by the rollers 12 while the screw a is transferred to the lower ends thereof. When a screw whose head diameter is smaller than the tolerance is transferred from the upper ends, this screw drops from an upper zone Z1 between the rollers 12 while being transferred. When a screw whose head diameter is within the tolerance is transferred, this screw drops from an intermediate zone Z2 between the rollers 12. Further, when a screw whose head diameter is larger than the tolerance, the screw drops from a lower zone Z3 between the rollers 12. In this manner, the screws a are classified into three types: the screw whose head diameter is smaller than, within, and larger than the predetermined tolerance. As apparent from the above description, this roller type sorter 10 is a device for inspecting the head size of the screws a with simple construction and easy handling.
FIG. 2 shows a conventional screw inspection device which is capable of performing various inspections on the screw, incorporating other sensors (not shown) and including the roller type sorter 10. The screw inspection device 13 of FIG. 2 comprises the roller type sorter 10, a first parts feeder 14 which feeds the screw a to the roller type sorter 10, a second parts feeder 15 which stacks the screw a the head of which has a diameter within the tolerance and which is dropped from the intermediate zone Z2, a linear feeder 16 which is disposed in the screw feeding side of the second parts feeder 15, a rotating table 17 which is disposed in the screw feeding side of the linear feeder 16, and a plurality of inspection units (not shown) such as various transfer mechanisms and sensors which are arranged around the rotating table 17. The sensors, for example, are sensors for detecting the shank length of the screw a, the presence or absence of threads of the screw a, and detecting whether or not plating is performed well. The screw inspection device with the above structure works effectively. However, many problems must be solved. For example, the smooth transfer of the screw a from the linear feeder 16 to the rotating table 17 is not well accomplished. Further, the transfer operations between other transfer mechanisms are not efficiently and smoothly accomplished. The rough transfer operation results in mechanical trouble. When the screw inspection device 13 breaks down, the operation thereof must be interrupted in order to repair a broken part, thus shortening the operation time. Further, in addition to the roller type sorter 10, the two parts feeders 14 and 15, the linear feeder 16, the rotating table 17 and the like are required, resulting in a complex structure with a high manufacturing cost. Further, every time the kind of screw changes, the roller type sorter must be adjusted, resulting in inconvenience.